1. Field of the Invention
This invention relates to a method for the production of a slide fastener or stringers thereof having coupling elements made of copper or a copper alloy.
2. Description of the Prior Art
Heretofore, in the slide fastener or the stringers thereof having coupling elements made of copper or a copper alloy, the coupling elements made of copper or a copper alloy are generally formed by sequentially cutting a multiplicity of coupling element blanks 2' of a prescribed thickness from a linear material 1 made of copper or a copper alloy and possessed of a prescribed sectional shape conforming to the shape of coupling elements as illustrated in FIG. 1 and then imparting meshing or engaging depressions 3 and meshing or engaging projections 4 by the forming punch to the opposite faces of the coupling element blanks as illustrated in FIG. 2 and the coupling elements 2 thus cut and formed are sequentially fixed as spaced with a prescribed interval on the longitudinal edge of a fastener tape 5. As a result, such marks of cutting as undulating notches produced on outer faces 2a of the coupling elements 2 and burred parts produced on edge parts 2b thereof during the process of cutting the linear material 1 mentioned above persist on the coupling elements and compel the coupling elements to give an objectionable prickly touch. A slide fastener which is fabricated with these coupling elements 2 has the problem that a slider thereof is not smoothly moved when the two stringers thereof are mutually engaged or disengaged. Further, since the coupling elements are made of copper or a copper alloy, they have the problem that they offer no resistance to corrosion and easily yield their outer faces to oxidation and discoloration.
As means for improving the touch of the coupling elements or the ease of motion of the slider and as means for improving the resistance of the coupling elements to corrosion, the method of chemical polishing treatment which comprises chemically polishing the undulating parts on the outer faces of the coupling elements has been known. The chemical polishing treatment generally uses a chemical polishing liquid which contains hydrogen peroxide and sulfuric acid. It is implemented by wholly immersing in the chemical polishing liquid the slide fastener stringers having the coupling elements made of copper or a copper alloy fixed as spaced with a prescribed interval to the longitudinal edges of the fastener tapes. According to this chemical polishing treatment, an oxide is formed on the surfaces of the coupling elements made of copper or a copper alloy and the undulating cutting marks on the outer surfaces of the coupling elements are smoothly flattened when the oxide is dissolved by the acid.
Such mechanical means as punches and dies are used when the multiplicity of coupling element blanks are cut from the linear material of copper or a copper alloy and the meshing depressions and meshing projections are formed on the surfaces of the coupling element blanks with a forming punch. As an inevitable consequence, cutting oil and machine oil adhere to the outer surfaces of the coupling elements and they tend to impair the evenness of the chemical polishing. These coupling elements, therefore, must undergo a degreasing treatment with an aqueous alkali solution prior to the chemical polishing treatment. Since the chemical polishing liquid is an acidic liquid, the coupling elements which have undergone the degreasing treatment must be given a neutralizing treatment prior to the chemical polishing treatment. Further, when the coupling elements made of copper or a copper alloy are chemically polished with a treating liquid containing hydrogen peroxide, they require a step of washing with an acid (pickling step) for the removal of the skin of copper oxide (CuO) which is formed on the outer surfaces of the coupling elements.
When the slide fastener stringers having the coupling elements of copper or a copper alloy are subjected to the chemical polishing treatment, therefore, they need to be first degreased with an alkali, washed with water, neutralized (as with sulfuric acid), washed with water, chemically polished by immersion in the chemical polishing liquid, washed with water, further washed with acid (sulfuric acid), and washed with water. The chemical polishing treatment, therefore, is problematic in terms of cost because the number of component steps is so large as to boost the cost of materials and the cost of energy required for the steps. Further, the fact that the number of component steps is so large as mentioned above has entrained such problems as discoloring the fastener tapes dyed in advance and deteriorating the materials thereof.
Besides, the chemical polishing treatment by the use of the liquid containing hydrogen peroxide as mentioned above has the problem that the hydrogen peroxide during the treatment undergoes decomposition with evolution of bubbles and the produced bubbles adhere to the outer surfaces of the coupling elements and, as a result, disrupt the evenness of the chemical polishing.